Abstract: A dual chamber side air bag apparatus may include an inflator mounted to a side of a sheet bag frame in an outdoor direction, an air bag cushion fluid-connected to the inflator and including a first chamber and a second chamber mounted at a side of the sheet bag frame in the outdoor direction and fluid-connected to the inflator and the first chamber to protrude and develop toward a front of the sheet bag frame when the inflator may be activated, for protecting side surface of the upper body of the passenger, and a tedder having one end thereof fixed to the sheet bag frame, a mid portion thereof wrapping the first chamber, and the other end thereof sewing-coupled to the air bag cushion in a boundary of the first and second chambers to provide a directivity so that the first chamber develops toward the upper body of the passengers.